Comparison of Common White Sucker and Longnose Sucker Population Changes: Long-Term Evaluation, 1980-2013 by Annalise M

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Comparison of Common White Sucker and Longnose Sucker Population Changes: Long-term evaluation, 1980-2013 By Annalise M. Povolo, Randall M. Claramunt and David F. Clapp Michigan Department of Natural Resources, Charlevoix Great Lakes Station, 96 Grant Street, Charlevoix, MI 49720

Background: Recently, there has been concern that sucker Catostomidae abundances have severely decreased throughout the Great Lakes. Potential explanations for the decline relate to interactions with invasive species, and include low zooplankton availability after the introduction of dreissenids, as well as top-down effects in which young-of-the-year (YOY) suckers are preyed on more heavily because of a decline in alewife populations. Long-term data collected during bottom gill net surveys from the Michigan Department of Natural Resources’ Survey Vessel Steelhead have made it possible to analyze the long- and short-term trends in common white sucker (CWS) Catostomus commersonii and longnose sucker (LNS) Catostomus catostomus abundances and sizes in Lake Michigan.

Major Findings: 1. Long-term abundances: Measures of catch-per-effort (CPE) show there is a fluctuating pattern in CWS and LNS abundances over time. As evident by the linear trend lines, there was a long-term trend from 1980 until 2002 in which the CPE of LNS was on average 1.3 fish/1000 ft lower than the CWS. Near the end of this series of higher CWS abundance, the CPE of LNS peaked at 5.2 fish/1000 ft while CWS remained lower at 1.6 fish/1000 ft from 1995 to 1999. This was followed by another fluctuation from 1999 to 2002 with CWS CPE reaching 4.6 fish/1000 ft and LNS CPE remaining lower around 2.7 fish/1000 ft. Since the CWS peak around 2002, the abundance of LNS has been close to or higher than CWS abundance, and appears to be continuing in this trend. It is evident from the long-term abundances that fluctuating patterns exist in which one sucker species is more abundant than the other, however, there is no significant overall correlation in the CPE between the two species. This lack of correlation indicates that longnose sucker and common white sucker populations are independent of each other.

6 CWS

5 Dreissenids LNS introduced 4

2 CPE CPE (#/1000 ft) 1

Sample Year

2. Effect of invasive species on abundance: The introduction and subsequent spread of dreissenids occurred in the late 1980s to the early 1990s. Bottom gill nets were not used during the years of 1991 through 1994, although there was a period of low sucker abundance immediately following the introduction of dreissenids, followed by a period of high abundances for both species after the years of missing data. Combining CPE for both species before the introduction of dreissenids and after showed no distinct change in average CPE of suckers, with the pre-dreissenid combined CPE at 3.2 fish/1000 ft and the post-dreissenid combined CPE at 3.1 fish/1000 ft. Even though the total abundance has not changed during the two time series, it appears as though environmental conditions have favored LNS in the recent time series. Additional monitoring will help determine whether or not this is indicative of a long-term trend.

3. CWS and LNS mean lengths: The mean lengths of common white suckers and longnose suckers have fluctuated at similar intervals from 1997 to 2002. After 2002, the mean length of LNS continued in this pattern of fluctuation, but as evident from the linear trend lines, also showed an increasing trend in mean lengths. The mean length of CWS throughout this time period has also increased, but at a slower rate and with greater variation. Although this fluctuating pattern exists, there is still no significant correlation between the mean lengths of common white suckers and longnose suckers.

CWS 500 LNS

480

460

440

420 MeanLength(mm) 400

380

Sample Year

*No complete biodata was available before 1997.

Results:

 The common white sucker mean CPE ranged from 0 to 5.3 fish/1000 ft and averaged 1.9 ± 1.7 fish/1000 ft across the 1980-2013 time series. In 2013, CPE decreased from 2012 and was 0.4 times lower than the average for the long-term data series.  The longnose sucker mean CPE ranged from 0 to 5.2 fish/1000 ft and averaged 1.3 ± 1.1 fish/1000 ft across the 1980-2013 time series. In 2013, CPE increased from 2012 and was almost equal to the average for the long-term data series.  The common white sucker mean length ranged from 400 to 479 mm and averaged 438 mm ± 28 mm across the 1997-2013 time series. In 2013 mean length increased from 2012 and was slightly higher than the average from the long-term data series.  The longnose sucker mean length ranged from 418 to 483 and averaged 450 mm ± 24 mm across the 1997-2013 time series. In 2013 the mean length increased from 2012 and was slightly higher than the average from the long-term data series.

Conclusions:

 The relative abundance and mean length of the common white sucker are independent from those of the longnose sucker.  Relative abundance of suckers does not seem to be substantially impacted by invasive species (i.e. dreissenids) or at least does not seem to have a short-term impact.  Because of repeated short- and long-term fluctuations, there should not be concern about sucker populations in Lake Michigan. However, all information has come from surveys that have not specifically targeted suckers. More intensive sucker surveys would improve our understanding of sucker populations in the Great Lakes.